Industry standards organizations figured out three decades ago when developing the first twisted-pair cabling standards that at the maximum frequency for a given application and length, certain performance parameters impacted the ability of the signal to properly reach or be interpreted by the far end. Insertion loss i. This reduction of signal happens along any length of cable for any type of transmission—and the longer the length, the greater the loss. Based on these performance parameters, industry standards standardized on the m distance and have stuck with it even as new applications with higher frequencies and new cable constructions were introduced.
It has significantly simplified the development of performance specifications. Think about it. Another performance parameter related to length is propagation delay—the amount of time it takes for a transmitted signal to be received at the far end. In twisted-pair cabling, delay is related to the nominal velocity of propagation NVP , as well as the length of the cable and the operating frequency.
NVP characterizes how fast a signal travels down the cable relative to the speed of light in a vacuum and there is a maximum that can be supported without loss of signal. Due to various pair twists, the delay can be different across pairs, which is a problem when multiple pairs are carrying data. The difference between the pair with the least delay and the pair with the greatest delay calculated as propagation delay skew must be low enough for network equipment to properly interpret the signal, and longer lengths can exasperate the difference.
Now you know that the m distance limitation relates to several factors—frequency, insertion loss, resistance, temperature and propagation all mixed in with a little history. Transmission speed has a lot to do with extended-length cables. Since standards are based on worst-case scenario and minimally compliant components, most reputable cabling and connectivity vendors already offer headroom by exceeding the standards.
Many devices that need to extend beyond the m distance are also lower-speed devices such as access control devices think parking lot entrance gates , emergency call boxes like you see on college campuses , and security cameras like the one at the far corner of the warehouse.
One way to support extended lengths is to use a cable capable of supporting a much higher bandwidth than the device requires. There are also characteristics of cable that impact length, such as conductor size, shielding, pair twist and even the dielectric material that form any insulation and cable jacket. Since larger gauge wires have less resistance and therefore better insertion loss, some extended-length cables feature 22 or 23 AWG conductors rather than 24 AWG. DC resistance unbalance also comes into play—if the difference in DC resistance between two conductors is too high, common mode voltage such as PoE is not equally split, which can further distort data signals.
So many extended-length cables are also carefully manufactured to ensure good DC resistance unbalance performance. Remember that heat can also impact insertion loss. Since shielded cables can better dissipate heat associated with temperature build-up from PoE and surrounding ambient temperature, some extended-length cables are also shielded. Fully-shielded cables may be able to support even greater distances.
If you choose to deploy an extended-reach cable, first understand that the installation will not be standards compliant. I think it is actually 90 meters?
The remaining ten meters is to account in the 5m patch leads at both ends. I could have a single cable that connects a PC to a switch, and that could be meters ignoring the differences between solid-core and stranded cable. The solid-core cable has better performance, but is fragile and can't be moved a lot.
The stranded cable is less fragile but has poorer performance. The total length is limited to meters. I would say"fragile" is a great exaggeration. Stranded copper is much more resilient to bends and movement even if individual strands break the "weave" of the strands maintains continuity.
Kevin Kevin 1. The question is about using Base-T in full duplex mode. You can't even buy any equipment supporting HDX at gigabit. You are not answering the question All 8 wires are normally only used for PoE. JonRhoades, you are in correct. If you try to connect at 1 Gbps with less that four pairs, you will only connect at Mbps. Ron "you will only connect at Mbps" - if at all; fallback is not by standard and only done by some vendors.
Zac67, as Ricky Beam pointed out a while back from testing, some of the early BASE-T chipsets were capable of this auto-negotiation, but there was a bug that prevented it from working. Show 3 more comments. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Explaining the semiconductor shortage, and how it might end. Does ES6 make JavaScript frameworks obsolete?
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